1. Field of the Invention
The present invention relates to an ion generator for use in an ion implantation apparatus, an ion repair apparatus, an ion etching apparatus, or the like.
2. Description of the Related Art
In an ion generator of this type, a voltage is applied between a filament and an anode, a predetermined gas is introduced between the electrodes to produce a plasma, and certain ions are collected from the plasma. A Freeman-type ion generator is well-known as this type of ion generator and is widely used in the art.
In Published Unexamined Japanese Patent Application (PUJPA) No. 62-278736 filed by the same assignee as this case, an ion generator used for electron beam excitation is proposed. In this ion generator, a voltage is applied between a filament and an anode, to thereby produce a first plasma from a predetermined gas, and then electrons are collected from the first plasma. An ion-generating gas is introduced into an ion-generating chamber and is irradiated with the electrons collected from the first plasma, to thereby produce a second plasma. The ions contained in the second plasma are collected through an ion output slit of the ion-generating chamber.
The ion generator mentioned in the preceding paragraph is advantageous, in that a high ion-current density can be obtained with a small amount of ion energy.
In an ion generator, it is likely that the structural components exposed to a plasma will be worn away since the ions of the plasma have sputtering and etching effects on such structural components. It is also likely that the substance produced by sputtering will adhere to, or be deposited on the structural components. This being so, the ion generator has to be maintained regularly. For instance, it has to be regularly cleaned or its structural components have to be regularly replaced with new ones.
If the ion generator uses a material gas which has a high degree of etching characteristic, the structural components of the ion generator will be markedly worn away, and the substance produced by sputtering will be deposited over the structural components in large quantities. Let it be assumed that an ion-generating chamber is formed of molybdenum and that the material gas is BF.sub.3. In this case, an insulating material, such as molybdenum fluoride, attaches to the surface of the ion-collecting electrode, thus adversely affecting the function of this electrode.
The ions generated in the ion-generating chamber pass through the ion output slit. Therefore, the structural component in which the ion output slit is formed wears away most noticeably than the other structural components of the ion generator. Since the structural component having the ion output slit is integral with the other portions of the ion-generating chamber, the ion-generating chamber has to be regularly replaced with a new one.
In the ion generator, the voltage applied between the ion-generating chamber and the ion-collecting electrode is as high as 32 KV or so. Due to the application of such a high voltage, a spark discharge may occur. If a spark discharge occurs, the structural components are damaged.
Conventionally, the ion generator has been cleaned in the manner below. First, the ion generator is switched off, so as to bring the highly-vacuum regions inside the ion generator into a normal-pressure state. Then, the contaminated portions of the ion generator are manually cleaned or polished. Since this operation is performed with respect to the portions which are difficult of access, it requires much time and labor. This results in a decrease in the rate of operation of the ion generator, and the productivity is lowered, accordingly.